Shell structure from 100Sn to 78Ni:: Implications for nuclear astrophysics

The single-particle structure and shell gap of Sn-100 is inferred from prompt in-beam and delayed gamma-ray spectroscopy of seniority and spin-gap isomers. Recent results in Ag-94,Ag-65 and Cd-98 stress the importance of large-scale shell model calculations employing realistic interactions for the isomerism, np-nh excitations and E2 polarisation of the Sn-100 core. The strong monopole interaction of the Delta l = 0 spin-flip partners pi g(9/2)-nu g(7/2) in N = 51 isotones below Sn-100 is echoed in the Delta l = 1 pi f(5/2)-nu g(9/2) pair of nucleons, which is decisive for the persistence of the N = 50 shell gap in Ni-78. This is corroborated by recent experimental data on Ni-70,Ni-76, Zn-78. The importance of monopole driven shell evolution for the appearance of new shell closures in neutron-rich nuclei and implications for r-process abundances near the N = 82 shell is discussed.